The 1993 World Trade Center case serves as an example of how seemingly bumbling grassroots jihadists or "Kramer Terrorists" can become quite deadly when they link up with a highly trained terrorist facilitator who can lead and organize them.

It is far harder for jihadist groups such as al Qaeda or the Islamic State to conduct a 9/11-style attack using highly trained operatives dispatched from overseas to conduct attacks in the United States and the West. The big difference between 1993 and today is that we are now acutely aware of who the jihadists are, be they members of al Qaeda, the Islamic State or other organizations. We also know what they believe and have a clearer idea of their capabilities. There is much more emphasis on countering the threat than there was in 1993. Security agencies also have more resources now.

Such groups have long struggled to survive inside China’s ill-defined, shifting margins of official tolerance, but they have served as havens for socially committed citizens. Under President Xi Jinping, however, the Communist Party has forcefully narrowed the bounds of accepted activity, setting off fears that these pockets of greater openness in China’s generally restrictive political landscape may soon disappear.

You can make your arguments online, or write articles criticizing the government, but once you mobilize people you’re going to have some serious problems,” Mr. Guo said in an interview shortly after Mr. Xu was arrested in the summer of 2013 for organizing street protests against official corruption

According to the standard definition, an optimal currency area is characterized by perfect labor mobility, perfect wage flexibility, and a risk-sharing system, such as fiscal transfers when a region — or a member country — is affected by an economic or financial shock.

Within the current system, member states are locked into fixed exchange rates, which reflect the conversion rate of national currencies into the euro. The exchange rate can no longer be used as a policy tool to make exports more competitive and rebalance the domestic economy. Thus, a country can only achieve competitiveness in the short run by deflating wages and reducing labor costs.

None of this should have been a surprise. The euro project isn’t the first time a fixed exchange rate has forced countries to rebalance through painful and pointless deflation. Before World War I and briefly afterward, the global economy worked on the gold standard, which functioned globally much the same way the euro does within the 19 countries that use it as their currency. As a result of the Great Depression, countries could no longer cope with the reductions in prices and wages necessary to maintain competitiveness, and they began to leave the gold standard. Britain left in 1931 when it became clear that the sterling’s exchange rate was too high and was pushing unemployment up.

Europe’s monetary union is a political project built on the impossible assumption that a single currency — and a single market — can transcend national interests and domestic politics.